High speed impact print hammer assembly with resilient energy storing means



Aug. 16, 1966 A. c. ERPEL ET AL 3,266,419

HIGH SPEED IMPAQT PRINT HAMMER ASSEMBLY WITH RESILIENT ENERGY STORING MEANS Original Filed Aug. 11. 1964 INVENTORS ADOLPH c. ERPEL JOHN PAUL JONES,JR.

ATTORNEYS United States Patent 3,266,419 HIGH SPEED IMPACT PRHNT HAMMER ASSEMBLY WITH RESILIENT ENERGY STQRING MEANS Adolph C. Erpel, Warrington, and John Paul Jones, Jr., Wynnewood, Pa., assignors to Navigation Computer Corporation, Norristown, Pa., a corporation of Pennsylvania Original application Aug. 11, 1964, Ser. No. 388,893, now Patent No. 3,232,404, dated Feb. 1, 1966. Divided and this application Oct. 5, 1965, Ser. No. 495,025 (Filed under Rule 45(c) and 35 U.S.C. 116) 2 Claims. (Cl. 101-93) This is a division under Rule 45 (c) of the copending application, Serial No. 388,893, for Keyboard Operated Printer, filed Aug. 11, 1964, now Patent No. 3,232,404. This invention relates to printing mechanisms and, more particularly, it relates to impact type printers for striking continuously rotating printiwheels.

While prior art systems have been proposed for electronic controls to print from a continuously rotating type wheel, such systems have involved complex timing means to produce exact timing of contact by the printing hammer in synchronization with the type characters presented by the wheel to prevent jitter of type spacing within the tolerances of the system parameters. The effect of the speed of the type wheel, the coding and commutating devices, the print hammer operating characteristics, the driving energy and resulting timing variations of the print hammer with lubrication, voltage resistance, etc., all tend to produce accumulative error of printing tolerances, thus holding down printing speed attainable with printed characters spaced within tolerances satisfying human visual observation.

It is therefore an object of the present invention to provide improved impact printer means which operate at high enough speeds to simplify system tolerances, and eliminate jitter and accumulated timing errors.

While prior artsystems have provided hammer mechanisms which drive free flying hammer pins into a continuously rotating typewheel, various problems have been encountered which prevent satisfactory use of such printers without complex auxiliary electronic or mechanical timing controls to reduce jitter, smear, and timing errors. Thus, in those systems providing mechanical cam operation for driving print hammer pins, the speed of impact of the hammer against the type is limited by gradual acceleration of the .driving means resulting in smear and jitter at high typewheel speeds. Also, precise electrical timing with electronic systems is difiicult, being dependent upon mechanical cycles and thus large timing tolerances.

These deficiencies have, in part, been corrected by use of electromagnetically controlled relay impact means for operating the print hammer so that electronic timing devices may be used to actuate the relay. However, relays have significant inductance and very slow gradual closing characteristics which can introduce long delays and unpredictable tolerances into impact timing with resultant jitter and bounce showing up in the print. Furthermore, the inertia of the relay tends to hold the hammer in contact with the print wheel introducing smear. In part this has been corrected by introduction of free-flying pin hammers which are projected by impact from a relay armature. An example of such high speed printers is shown in Shepard Patent 2,787,210, issued April 2, 195 7. Even in these devices, however, timing is critical and engineering design must be confined to carefully relate relay and pin contfigurations to a particular typewheel speed to prevent smear.

An improved printing assembly is therefore provided .by the present invention producing less critical timing with simplified mechanical and electronic design requirements. In essence, the print assembly provides an extremely high speed flying-pin type hammer propelled from an electromagnetic relay armature in response to an electrical impulse which can be timed to conform with external system requirements. Not only is high impact speed provided :but also high return speed, so that contact with the typewheel takes place over very few microseconds, and thus variations in print spacing, jitter and smear is essentially eliminated. This results from a simple mechanical bounce-back interposer external to the typewheel meeting the free-flying pin at the moment it contacts the type-' wheel to forcibly return it. In this manner the return force is made independent of the material in the typewheel, the speed of the wheel or the area of the character being printed, etc., and is simply designed without significant cost to produce optimum high speed return of the hammer pin after striking the type with extremely high force during a very short period of time, thereby not necessitating any compromise in time of dwell to obtain a favorable print characteristic, nor requiring a particular type Wheel elasticity, etc.

The construction of the print assembly thus afforded by the invention is illustrated in the drawing by a schematic representation of a printer assembly constructed in accordance with the principles of this invention.

As shown in the drawing, the printer mechanism serves to strike a continuously rotating type wheel 10 with a print pin or hammer 94 to produce a printed character on paper 96 from interspersed carbon paper 95. The type wheel may rotate at speeds of from ten to thirty revolutions per second to present alphanumeric type characters typically each millisecond.

In order to produce substantially jitter-free printout and increased system tolerances in speed of the typewheel 10 and motion of the paper 95 and 96 with the impact of a mechanically operated hammer, it is necessary not only to strike the printwheel with the print hammer at high impact speed, but also to retract the print hammer quickly to avoid smear or bounce.

High impact speed is attained by using a free-flying hammer pin 94, which has only a weak spring 97 for holding it in rest or retracted position with yoke 98, which defines the limitations of the pin stroke by resting at one end against pin housing 99 to await impact by the elastic driving member 91, which is a button of hardened steel positioned upon relay armature '89. Accordingly, relay coil 88 is energized by an electronic pulse to quickly close armature 89 through the very small magnetic gap 90 to drive the hammer pin 94 as it partially closes the gap to rapidly drive it into the type wheel -10 at very high speed in the same manner as a golf ball is driven from a tee, rather than in a gradual contact as provided by cam actuated hammers or those directly coupled for drive by the relay armature. The rounded and hardened head of pin 94 meets button 91 in almost pure elastic contact to send almost all of the driving energy int-o the longitudinal motion of the hammer pin 94, through its confined stroke path provided by casing 99.

Since the paper layers 95 and 96 are thin, the driving range of the hammer pin 94 is small, and the magnetic gap 90 in the relay need not be that thick to place the pin 94 in free-fly motion, operational speed is significantly increased over normal large gap spacings which must move the pin the entire distance into the paper by operation of a square law factor associated with the gap spacing. In other words, not only is the mechanical impact speed of a free fiying pin increased in this embodiment, but also the electrical operational speed is increased by reducing the time it takes to signal the relay to impact the hammer pin with its reduced length of stroke. It is also noted that the armature 89 is light with little mechanical inertia as compared with that of a complete assembly including a hammer coupled to the armature, thus further contributing to high speed operation. Even spring 8 5 biasing the armature into its open position is light and need not seriously handicap operation speed since the mass of the armature is small. A typical operating speed of less than a half millisecond is thus provided in the relay as compared with an order of magnitude greater time with increased gap distances presenting greater electrical and mechanical inertia. Even greater improvement is produced over cases where the hammer and relay armature are integral.

Quick return of the hammer pin 94 from the flying typewheel cannot be attained from weak spring 97 without significantly reducing free-[fly speed of the hammer pin 94 and impact speed with the type wheel. Thus, a rubber or resilient plastic bumper member 93 is positioned to intercept the yoke 98 of the hammer pin 94 just as it strikes the print wheel to thereby produce a significant amount of return stroke energy. Because of the freefiying pin 94 configuration with rubber bumper 93 a complete print hammer stroke may be accomplished in the order of a few microseconds, thereby producing very high print speeds without jitter or smear from a continuously rotating Wheel. This construction is simple, takes up essentially no extra space and does not confine the other engineering parameters of the system in any Way by requiring optimum speeds or dimensions of the flying hammer pin 94, or the length of time armature 89 is in contact with hammer pin 94. Adjusting screw assembly 87 is provided for adjusting the magnetic gap 90 of the relay where desired to produce an optimized operation of each printer assembly. Similarly, screw assembly 8 6 can be used to precisely adjust the position of rubber bumper block 93 to account for mechanical variations in print assemblies.

Accordingly, a print hammer assembly is provided by this invention which works in combination to produce high speed jitter-free printing from a continuously rotating typewheel. Therefore, the features of the hammer assembly which combine to give the improved performance are defined with particularity in the appended claims which are believed to define the nature and scope of the invention.

What is claimed is:

1. A print assembly for impacting a continuously rotating typewheel comprising in combination,

a movable electromagnetic armature,

a relay for moving said armature responsive to electronic signals,

a housing, said housing forming an enclosure having opposite end walls with apertures therein, means for relatively positioning one of said end walls,

a movable hammer pin having an integral yoke member located within said enclosure, said hammer pin having two stems, each of said stems projecting through an aperture in one of said opposite end walls, one stem opposite the relatively positionable end wall being positioned for intercepting and receiving the impact of said movable armature,

an energy storing resilient bumper positioned upon the relatively positionable said end wall to intercept said yoke,

the movement of said hammer pin being confined by said yoke in a longitudinal stroke path defined by contact at two limiting positions at said resilient bumper and the other opposite end wall,

spring means positioned in said enclosure surrounding said pin for weakly biasing said yoke toward the one of said limiting positions away from said resilient bumper,

said means relatively positioning one of said end walls being adjusted to receive the impact of the pin yoke momentarily at one end of the stroke path to coincide With the pin striking said typewheel to print a character therefrom and quickly retract said pin from contact with said typewheel by means of energy stored in said bumper.

2. A print assembly as defined in claim 1 providing a very small magnetic gap between said armature and said relay, and with a spacing between the one of said stems receiving the armature impact and said armature to permit impact afiter the armature has partially closed said gap.

References Cited by the Examiner UNiTED STATES PATENTS 2,787,210 4/1957 Shepard 10193 2,874,634 2/1959 He-nse 10193 3,090,297 5/1963 Wilkens et al 10l-93 3,115,092 12/1963 Sosaki 10193 3,139,820 7/1964 Kittler l0193 3,144,821 8/1964 Drejza 10193 3,152,540 10/1964 Pensavecchia et al. 101-93 3,183,830 5/1965 Fisher et a1 10193 3,195,453 7/1965 Thiemann 101-93 ROBERT E. PUDFREY, Primary Examiner.

DAVID KLEIN, Examiner.

E. S. B-URR, Assistant Examiner. 

1. A PRINT ASSEMBLY FOR IMPACTING A CONTINUOUSLY ROTATING TYPEWHEEL COMPRISING IN COMBINATION, A MOVABLE ELECTROMAGNETIC ARMATURE, A RELAY FOR MOVING SAID ARMATURE RESPONSIVE TO ELECTRONIC SIGNALS, A HOUSING, SAID HOUSING FORMING AN ENCLOSURE HAVING OPPOSITE END WALLS WITH APERTURESTHEREIN, MEANS FOR RELATIVELY POSITIONING ONE OF SAID END WALLS, A MOVABLE HAMMER PIN HAVING AN INTEGRAL YOKE MEMBER LOCATED WITHIN SAID ENCLOSURE, SAID HAMMER PIN HAVING TWO STEMS, EACH OF SAID STEMS PROJECTING THROUGH AN APERTURE IN ONE OF SAID OPPOSITE END WALLS, ONE STEM OPPOSITE THE RELATIVELY POSITIONABLE END WALL BEING POSITIONED FOR INTERCEPTING AND RECEIVING THE IMPACT OF SAID MOVABLE ARMATURE, AN ENERGY STORING RESILIENT BUMPER POSITIONED UPON THE RELATIVELY POSITIONABLE SAID END WALL TO INTERCEPT SAID YOKE, THE MOVEMENT OF SAID HAMMER PIN BEING CONFINED BY SAID YOKE IN A LONGITUDINAL STROKE PATH DEFINED BY CONTACT AT TWO LIMITING POSITIONS AT SAID RESILIENT BUMPER AND THE OTHER OPPOSITE END WALL, SPRING MEANS POSITIONED IN SAID ENCLOSURE SURROUNDING SAID PIN FOR WEAKLY BIASING SAID YOKE TOWARD THE ONE OF SAID LIMITING POSITIONS AWAY FROM SAID RESILIENT BUMPER, SAID MEANS RELATIVELY POSITIONING ONE OF SAID END WALLS BEING ADJUSTED TO RECEIVE THE IMPACT OF THE PIN YOKE MOMENTARILY AT ONE END OF THE STROKE PATH TO COINCIDE WITH THE PIN STRIKING SAID TYPEWHEEL TO PRINT A CHARACTER THEREFROM AND QUICKLY RETRACT SAID PIN FROM CONTACT WITH SAID TYPEWHEEL BY MEANS OF ENERGY STORED IN SAID BUMPER. 